1. Field of the Invention
The present invention relates to a refrigerating system incorporating therein a variable capacity refrigerant compressor of the type having a reciprocating piston mechanism, for compressing a refrigerant gas, and a swash plate element capable of changing its inclination angle for varying the stroke of the pistons in response to a change in the pressure prevailing in the crank chamber of the compressor. More particularly, the present invention relates to a refrigerating system incorporating a variable capacity type compressor to compress a refrigerant and air-condition an automobile compartment.
2. Description of the Related Art
A conventional refrigerating system for automobiles generally includes a refrigerant flow conduit incorporating therein a condenser, a liquid receiver, an expansion valve (pressure reducer), an evaporator, and a variable capacity compressor such as a wobble plate type variable capacity compressor, or a swash plate type variable capacity compressor.
The variable capacity compressors used in the conventional automobile refrigerating system are driven by an automobile engine via a solenoid clutch, and compress a refrigerant gas by using pistons reciprocating in the cylinder bores thereof. The compressed refrigerant gas, at a high pressure and a high temperature is delivered to the condenser of the refrigerating system wherein the gas is liquified. The refrigerant liquid is subsequently delivered from the condenser to the expansion valve wherein the refrigerant liquid is subjected to adiabatic expansion to be changed into a compound gas and liquid refrigerant at a low temperature and a low pressure. The compound refrigerant is further delivered to the evaporator wherein the compound refrigerant is evaporated by absorbing heat from the air around the evaporator to thereby cool the air which is destined to be distributed in the automobile compartment. The evaporated refrigerant in the gas phase then returns from the evaporator to the variable capacity compressor, as a low pressure refrigerant gas, via the refrigerant conduit.
The variable capacity refrigerant compressor used in the conventional refrigerating system is generally provided with a capacity control valve for controlling the amount of the compressed gas delivered by the variable capacity refrigerant compressor.
Particularly, the capacity control valve is provided to permit compressed gas at a high discharge pressure to selectively flow from the discharge chamber to the crank chamber of the compressor to thereby adjustably increase the pressure prevailing in the crank chamber in response to a change in the pressure of the refrigerant gas being sucked into the suction chamber of the compressor. When the pressure in the crank chamber is increased, the angle of inclination of the swash plate element of the compressor with respect to a plane perpendicular to the axis of the drive shaft of the compressor is reduced so as decrease the piston stroke of the pistons reciprocating in the cylinder bores and therefore, the amount of the compressed gas delivered by the compressor is reduced. It should be noted that a reduction in the delivery capacity of the compressed gas from the variable capacity compressor to the refrigerating system occurs either when the compressor is rotated at a high speed, or when the thermal load on the refrigerating system, including the compressor, is small. As a result, an amount of the refrigerant circulating through the refrigerating system is reduced, and accordingly, the refrigerant compressor must be exposed to undesirable operating conditions from the viewpoint of overheating and lack of lubrication of the compressor. Nevertheless, neither the compressor per se nor the conventional refrigerating system is provided with a means for preventing an occurrence of the above-mentioned undesirable operating conditions of the compressor.
Further, the solenoid clutch mounted on the external end of the drive shaft of the variable capacity refrigerant compressor is provided with a rotor rotatably held by the front housing of the variable capacity compressor which is driven by the automobile engine and an armature having an excitation coils arranged so as to confront the rotor. When the excitation coils are electrically energized, the armature is electro-magnetically attracted to the rotor, and accordingly, the drive power (torgue) is transmitted from the engine to the drive shaft of the compressor via the solenoid clutch. Thus, the operation of the compressor is started. However, the solenoid clutch arranged between the automobile engine and the drive shaft of the variable refrigerant compressor has various defects. Namely, since the solenoid clutch is heavy and expensive, the entire weight of the compressor with the solenoid clutch must be large and this entails an increase in the manufacturing cost of the compressor. Moreover, when the solenoid clutch is energized and de-energized, a sudden change in a load applied to the automobile engine occurs and, accordingly, can disturb the driver during the operation of the automobile. Further, it is necessary to increase the idling speed of the automobile engine in order to prevent stalling of the automobile engine due to the above-mentioned sudden change in the load applied to the automobile engine, and as a result, the fuel consumption of the automobile engine is increased. Further, the above-mentioned energizing of the excitation coils of the solenoid clutch often requires a lot of electric power, and therefore, the automobile must be equipped with an unduly large electric alternator. Thus, omission of the solenoid clutch arranged between the automobile engine and the drive shaft of the variable capacity refrigerant compressor is preferred.
In this regard, Japanese Unexamined Patent Publication No. 3-37378 discloses a non-clutch type variable capacity type compressor provided with a capacity control means for adjustably varying the amount of the compressed refrigerant gas delivered therefrom toward the refrigerating system in response to a change in the pressure of the refrigerant gas being sucked into the compressor. The compressor includes a cylinder block and a drive shaft having a pulley mounted on the external end thereof. The drive shaft is arranged so as to extend through a crank chamber formed in the cylinder block, and has a rotor element fixedly mounted thereon to rotate together with the drive shaft. A rotatable swash plate mechanism is supported by the rotor element via a hinge mechanism and by the drive shaft via a sleeve element. The swash plate mechanism is rotated within the crank chamber together with the drive shaft and can change its angle of inclination with respect to a plane perpendicular to the axis of rotation of the drive shaft. The swash plate mechanism includes nutating swash and wobble plate elements, and the wobble plate element is operatively connected to a plurality of single-headed pistons via respective piston rods. Thus, in response to the nutating motion of the wobble plate, the single-headed pistons reciprocate respectively in the corresponding cylinder bores. The compressor is further provided with a housing which defines a suction chamber for receiving a refrigerant gas, before compression, to be sucked into the respective cylinder bores, and a discharge chamber for receiving the refrigerant gas compressed in and discharged from the respective cylinder bores. The cylinder block and the housing are provided with a gas supply passageway formed therein for supplying the compressed gas from the discharge chamber to the crank chamber, and a gas extraction passageway formed therein for providing a fluid connection between the crank chamber and the suction chamber. The gas extraction passageway is provided with a choke or a throttle formed in a part thereof. The housing receives therein a capacity control valve having a pressure detecting bellows movable in response to a change in the pressure of the suction refrigerant gas and a valve element moving in response to the movement of the bellows to adjustably control the flow of the compressed refrigerant gas from the discharge chamber to the crank chamber.
The variable capacity non-clutch type compressor of Japanese Unexamined Patent Publication No. 3-37378 is characterized in that it includes a solenoid valve capable of controlling the opening area of a portion of an inlet passageway through which the suction refrigerant gas having returned from the evaporator of the refrigerating system is sucked into the suction chamber of the compressor.
The variable capacity non-clutch compressor can be driven by a drive force directly transmitting from an automobile engine via only a pulley mechanism without intervention of a solenoid clutch, and accordingly, once the automobile engine is started, the compressor immediately starts. During the running of the compressor, the capacity control valve constantly controls a pressure prevailing in the crank chamber of the compressor so as to adjustably change the angle of inclination of the swash plate mechanism to a required angle between the smallest and largest angles to thereby adjustably change a suction amount of the refrigerant gas and the delivered amount of the compressed refrigerant gas. During the running of the variable capacity non-clutch compressor, when the operation thereof to deliver the compressed refrigerant gas toward the refrigerating system is to be stopped, the above-mentioned solenoid valve is operated by an externally supplied signal so as to close the inlet passageway to thereby stop the suction of the refrigerant gas into the suction chamber. Accordingly, the pressure in the suction chamber falls and the capacity control valve reacts to the reduction in the suction pressure and immediately supplies the refrigerant gas at a high pressure from the discharge chamber to the crank chamber so as to increase the pressure prevailing in the crank chamber. As a result, the swash plate mechanism moves to the smallest angle position thereof at which the delivery capacity of the compressor becomes the minimum.
At this stage, when the delivered amount of the compressed refrigerant gas becomes a minimum, a small amount of the refrigerant gas compressed in the respective cylinder bores is discharged into the discharge chamber from the respective cylinder bores, and further flows toward the crank chamber through the gas supply passageway. Thereafter, the refrigerant gas entering the crank chamber further flows toward the suction chamber through the gas extraction passageway having the afore-mentioned choke. Nevertheless, this type of flow of the refrigerant gas circulating within the compressor from the respective cylinder bores to the suction chamber via the discharge chamber and the crank chamber is apparently different from the flow of the refrigerant passing through the refrigerating circuit. Therefore, it neither contributes to the cooling of the various moving elements of the compressor such as the swash plate, the wobble plate, shoes, and the shaft sealing devices nor achieves lubricating of the above-mentioned various moving elements if the suction of the refrigerant gas into the compressor is stopped, by the solenoid valve, at a time when the amount of lubricating oil held in the crank chamber of the compressor is reduced. Accordingly, the life of the non-clutch type refrigerant compressor is shortened.